Many effluent streams from industries are waste with no apparent beneficial use. However, environmental antipollution laws prohibit direct discharge of such streams to the environment because of the environmentally harmful materials they contain. Therefore, provision must be made for the safe disposal of such streams while confining or neutralizing their harmful effects.
Many different methods of disposal of liquid wastes have been devised. For example, both Cinner, U.S. Pat. No. 3,841,102, and Thompson, U.S. Pat. No. 3,980,558, treat liquid wastes with alkali metal silicates and/or cementitious material such as portland cement to solidify and entrap harmful components of the liquid wastes. Both Schleede, U.S. Pat. No. 3,978,673, and Dickson, U.S. Pat. No. 3,732,697, disclose disposal of liquid waste in loose earth, with Dickson further disclosing containment of such waste through use of a water impervious layer of compacted sandy clay soil. Tate, U.S. Pat. No. 3,817,859, disposes of industrial liquid wastes by injection into subterranean formations. Others have used deep wells for the disposal of industrial liquid wastes.
However, none of the above-mentioned technology is concerned with the ultimate recovery of any valuable substituents of such waste streams. For example, many caustic and acidic industrial waste streams such as spent pickling liquors contain low concentrations of various heavy metals such as chromium, aluminum, nickel, and cadmium. These metals would be valuable by-products of any liquid waste disposal system if they could be economically recovered. Accordingly, the need exists for a method of economically recovering valuable metals from liquid industrial waste streams while, at the same time providing for the environmentally safe disposal of such liquid wastes.